AT&T can easily spot customers that are using unauthorized tethering apps

In March, AT&T began cracking down on customers it
believed were jailbreaking their iPhones and using "unauthorized"
apps to tether data for no extra fee. Text messages were sent out to suspected
customers with an ultimatum: Stop tethering, or we'll automatically enroll you
in our $45 DataPro plan.

The folks
over at Android Policepoint out that
jailbroken iPhones are easy to pinpoint when tethered, because many tethering
apps use the same technique as the one inherent in iOS. When tethered, the
iPhone "sends traffic through an alternate APN (AT&T access
point/router) for the express purpose of identifying the traffic as tethered
data. This makes it extremely easy for AT&T to identify whether or not an
iOS device is utilizing tethering, and just how much of their data is consumed
via tethering."

The
customers AT&T is likely targeting most are those with the grandfathered
unlimited data plans. They can tether their hearts out, without worrying about
going over their allotted data cap.

IPhoneDownloadBlog has a list of iPhone
tethering apps. MyWi, the most popular one, uses the same APN as the iPhone's
standard tethering system, so it is not recommended if you want to go
undetected. Two other alternatives are PdaNet --
which offers a "hide" function -- and TetherMe.

However, some users in the comments section of iPhoneDownloadBlog are saying that even
with the updated versions of these tethering apps with hiding functionality enabled
can’t escape AT&T’s wrath.

“I used the new PDANET since the day it was released a few
weeks ago,” wrote one commenter. “Shortly after and consistent with 4.3 upgrade
I received an email from ATT.”

So perhaps no one is safe anymore when it comes to
unauthorized tethering on the iPhone.